450 RADioAcmi-: minerals in south Africa. 



In 1897 — i<S tons, value £210. 

 In 1898 — 23 tons, value £235. 



During the period 1895-1898 Brazil exported 5,350 tons of 

 nionazite. At that time monazite was solely used for the pre- 

 paration of thoric nitrate, required in the manufacture of the 

 mantles of incandescent lamps. As the production of monazite 

 rapidly increased, the price of thorium nitrate went down, the 

 cost of one kilogram being — 



In 1894 — iioo. 



In 1895 — i22. 



In 1896 — £3 IDS. 



In 1898— il 



In 1900 — £1 8s. 



Since 1900 the price of thoric nitrate has remained 

 stationary. 



Already in 1896 small quantities of monazite were observed 

 together with some other rare minerals like fergusonite and 

 seschynite in the alluvial tin ore deposits near Embabaan, in 

 Swaziland. In 1905 monazite was also discovered at Houten- 

 beck, in the Transvaal, together with fluorspar. The monazite 

 of these two South African localities has been investigated, 

 together with monazite from American localities, in the Chemical 

 Laboratory of the South African College. The deposit at 

 Houtenbeck was first reported upon in 1906 by Mr. Ernest 

 Williams, of Johannesburg. A small jmccc of this monazite 

 was sent to the author, who was then in Europe, and had this 

 specimen analysed in the Fresenius Laboratory at Wiesbaden : 

 it contained 2.3 per cent, of thoric dioxide. After his return 

 to South Africa the author secured a large quantity of the 

 Houtenbeck monazite. of which a number of analyses were 

 made. The results of analyses of five different pieces of 

 monazite from a large sample gave 1-44 per cent., 1.95 per 

 cent., 1.99 per cent., 2.14 per cent., and 3.23 per cent, of thoric 

 dioxide, yielding an average 2.15 per cent. The monazite of 

 Embabaan is richer in thoric dioxide ; three analyses made of 

 three different samples yielded 6.65 per cent, 6.80 per cent., and 

 7.02 per cent, of thoric dioxide, or an average of 6.82 per 

 cent. 



A similar dift'erence in the ])ercentage of thoric dioxide is 

 observed in the monazite sand from South Carolina, U.S.A., 

 and from Bahia, Brazil, the latter containing between i . 5 per 

 cent, and 3.5 per cent, of thoric dioxide, and the former on 

 an average 7 per cent. 



The impressions on the photographic plate produced by 

 the radio-activity of monazite are only faint after an exposure 

 of seven days ; they are a little more distinct after an exposure 

 of 15 days. Plate 12, a and b, show the radio-active eft'ect on 

 the photographic plate of monazite from Houtenbeck, and 



